For the purpose of inspecting a disconnection, short-circuit or the like in a circuit wiring (conductive pattern) formed on a circuit board, there has been employed a method including the steps of supplying an inspection signal to the circuit wiring, detecting the inspection signal at the end or another suitable position of the circuit wiring, optionally subjecting the detected signal to a suitable signal processing, and analyzing the detected signal.
The techniques for supplying an inspection signal to or detecting it from a circuit wiring may be broadly classified into a contact type in which the supply, detection or another process of the inspection signal is carried out in contact with the circuit wiring, and a non-contact type in which such a process is carried out in non-contact with the circuit wiring.
The contact type inspection has been widely known in which a probe composed of a conductive member such as a pin-shaped member is brought into contact with a circuit wiring to supply or detect an inspection signal through the probe.
On the other hand, the non-contact type inspection may be broadly classified into one type in which an inspection signal supplied to a circuit wiring is detected through a capacitive coupling between the circuit wiring and a sensor electrode, and the other type in which an electromagnetic field caused by an inspection signal supplied to a circuit wiring is detected.
With reference to FIG. 8, a principle of the former inspection based on the capacitive coupling will be described. FIG. 8(a) illustrates the principle of the inspection based on the capacitive coupling.
An inspection signal is supplied from a signal source 102 to one of the ends of a circuit wiring 100 to be inspected. Further, an electrode 101 is arranged in non-contact with the circuit wiring 100 at the other end of the circuit wiring 100. The signal source 102 is operable to generate an AC signal serving as the inspection signal and supply the generated signal to the one end of the circuit wiring 100 to be inspected. For the inspection signal, a temporally varied signal (e.g. a signal having a frequency in voltage variation ranging from about 1 kHz to about 10 MHz) is employed. As a substitute for the AC signal, a pulsed signal may be used.
In the illustrated structure, the electrode 101 and the other end of the circuit wiring 100 are capacitively coupled with each other to define a capacitor. Specifically, an equivalent circuit of FIG. 8(a) may be represented by FIG. 8(b). If the circuit wiring 100 has no disconnection, the electrode 101 can detect a signal caused thereat in response to an inspection signal supplied from the signal source 102 to the circuit wiring 100. Conversely, if the circuit wiring 100 has a disconnection, almost no signal will appear at the electrode 101. In this manner, the presence of disconnection in the circuit wiring 100 can be determined.
The aforementioned electrode 101 is exclusively used to detect the inspection signal. However, according to the same principle, if the signal source 102 is connected to the electrode 101, the electrode 101 is operable to supply an inspection signal to the circuit wiring 100. That is, the electrode 101 can be used not only to detect the inspection signal but also to supply it.
This inspection technique is advantageous in that the circuit wiring is seldom damaged because the electrode is in non-contact with the circuit wiring, and such an inspection technique has wide applicability to various circuit wirings including fine-pitch circuit wirings.
With reference to FIGS. 9 and 10, a principle of the inspection based on the detection of an electromagnetic field will be described below. FIGS. 9 and 10 illustrate the principle of this inspection.
The inspection based on the detection of an electromagnetic field is generally employed when the ends of circuit wirings to be inspected are connected with a short-circuiting wiring referred to as a short-circuiting bar. In FIG. 9, the ends of circuit wirings 112 to be inspected are connected with a short-circuiting wiring 111.
As shown in FIG. 9, when a certain potential is applied between a pair of adjacent circuit wirings 112, a current 113 will flow through these circuit wirings 112 and the short-circuiting wiring 111. As a result of the current 113, an electromagnetic field 114 is generated within the horseshoe-shaped region surrounded by these circuit wirings 112 and the short-circuiting wiring 111.
By detecting this electromagnetic field 114 with a magnetometric sensor composed of a coil, a hall element or the like, a defect in the pair of circuit wirings 112 applied with the potential difference can be determined. More specifically, for example, if there is a defect that the pair of the circuit wirings 112 are short-circuited by a line 115 as shown in FIG. 10, currents 113a and 113b will be caused because a part of the current 113 in FIG. 9 flows into the line 115, and correspondingly electromagnetic fields 114a and 114b will be generated.
Comparing the electromagnetic field 114a or 114b of FIG. 10 having the defect in the circuit wirings with the normal electromagnetic field 114 of FIG. 9, the former electromagnetic field has lower intensity because it is generated by the smaller current 113a or 113b. Thus, the presence of the defect in the circuit wirings can be determined by detecting the intensity, distribution or the like of the electromagnetic field within the region approximately surrounded by the pair of circuit wirings 112 to be inspected and the short-circuiting wiring 111.
As above, various techniques are proposed to inspect a circuit wiring, and each of the inspection techniques can be selectively applied depending on the specification of a circuit wiring to be inspected.
Further, for actually carrying out these inspection methods, an inspection unit referred to as a jig is used. The inspection unit includes a probe, electrode or the like arranged in conformity with a circuit wiring to be inspected. When a plurality of inspection methods are combinedly carried out, an inspection unit provided with a necessary probe, electrode and others will be used. FIG. 7(a) is a schematic diagram of a conventional inspection unit 200 including a probe for the contact type inspection, and an electrode for the inspection based on the capacitive coupling in the non-contact type inspection.
The inspection unit 200 comprises a baseboard 201, a reinforcing plate 202 laminated on the baseboard 201, a plurality of probe portions 203 each protruding from the surface of the reinforcing plate 202, and an electrode portion 204 provided on the reinforcing plate 202. A circuit board to be inspected is mounted on a platform 206, and each of locating pins 205 of the inspection unit 200 will be inserted into a corresponding one of holes of the circuit board and the platform 206 to place the inspection unit 200 on the circuit board.
FIG. 7(b) is a sectional view showing the structure of the inspection unit 200 around the probe portion 203. The probe portion 203 includes a probe body 203a, a sleeve 203b housing the rear end of the probe body 203a, and a spring 203c elastically biasing the probe body 203a in the axial direction of the probe body.
The sleeve 203b is fixedly attached to the baseboard 201. The probe body 203a is supported by the sleeve 203b through the spring 203 in a suspended manner, and is movable in the axial direction of the probe body 203a. Thus, when the inspection unit 200 is slightly pressed against the circuit board and placed thereon, the spring 203c biases the probe body 203a to allow the front end of the probe body to be reliably brought into contact with the circuit wiring.
The reinforcing plate 202 is composed of a plate member made by bakelite or the like, and is formed with a bore 202a for guiding the axial movement of the probe body 203a. This bore 202a is intended to support the probe body 203a with preventing undesirable misalignment caused when the probe body 203a is moved in its axial direction with being biased by the spring 203c. For this purpose, the bore 202a has a diameter slightly larger than that of the probe body 203a. 
FIG. 7(c) is a sectional view showing the structure of the inspection unit 200 around the electrode portion 204, particularly showing the structure around the electrode portion 204 which is arranged close to the probe portion 203.
The electrode portion 204 includes an electrode 204a composed of a copper thin film or the like, and a substrate 204b having the electrode 204a formed on the surface thereof. The electrode portion 204 is mounted on a hollowed portion of the reinforcing plate 202 with an adhesive, screw or the like.
However, due to the structure of the conventional inspection unit 200 in which the electrode portion 204 is mounted on the reinforcing plate 202, it has been difficult to assure a sufficient positioning accuracy between the probe portion 203 and the electrode portion 204.
Further, when the probe body 203a is arranged close to the electrode portion 204, or the probe body 203a is arranged to penetrate the electrode portion 204, as shown in FIG. 7(c), there is the case that the misalignment of the probe body 203a cannot be sufficiently prevented because the thickness of the bore 202a in the reinforcing plate 202 becomes thin due to the hollowed portion of the reinforcing plate 202 around the probe body 203a. In addtion, for machining the hollowed portion, it is necessary to assure a certain distance between the electrode 204a and the probe body 203a. This has set a limit to arrange the electrode 204a close to the probe body 203.
It is therefore an object of the present invention to provide an inspection unit and a method of manufacturing a board constituting such an inspection unit, capable of allowing a probe and other components to be positioned with a high degree of accuracy while preventing undesirable misalignment of the probe and to be arranged closer to each other.